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A TTORNEYS United States Patent 3,263,376 METHOD FOR SURFACING GLASS Emmett L. Walters, Richard E. Warren, Otto V. Young, and Martin Miklosek, Toledo, Ohio, assignors to Libbey-Owens-Ford Glass Company, Toledo, Ohio, a corporation of Ohio Original application Dec. 16, 1959, Ser. No. 859,919, new Patent No. 3,107,457, dated Oct. 22, 1963. Divided and this application Sept. 23, 1963, Ser. No. 320,944 2 Claims. (Cl. 5l283) This application is a division of application Serial No. 859,919, filed December 16, 1959, now Patent No. 3,107,- 457, dated October 22, 1963.

This invention broadly relates to a method for surfacing glass and more particularly to a method for simultaneously polishing both surfaces of a glass ribbon moving along a continuous path.

It has been long known that a glass ribbon may be ground on both sides, as for example according to the apparatus and process shown and described in US. Patent No. 2,176,481 issued to F. B. Waldron et al. on October 17, 1939. Circular rotating runners are normally employed rotating about a fixed axis, normally perpendicular to the glass, one runner being above and one runner being below the glass.

However, such a process for simultaneously grinding both surfaces of a glass ribbon has not proven to be entirely satisfactory. There is a tendency for the glass to break along the edges under the pressure of the rotating circular runners since they are unable to grind the glass uniformly across its width. This follows since these conventional circular runners perform less grinding action along the ribbon edges resulting in a somewhat uneven grinding pattern across the width of the ribbon. This uneven grinding pattern is of course, highly objectionable since in grinding a glass ribbon it is desirable to provide equal grinding action, or uniform grinding, on all points on the glass in order to both reduce the amount of grinding necessary to establish an absolutely flat surface and also to eliminate the possibility of developing excessive pressure at any point on the glass, which pressure would cause ribbon breakage.

Turning now to the present known polishing devices, it is also well known to polish both faces of a traveling strip of glass as shown and described in US. Patent No. 2,419,925 issued to F. B. Waldron et al. on April 29, 1947. In this concept the opposed surfaces are engaged by a plurality of circular polishing pads freely turnable about their individual axes, all being supported from a common frame that is itself rotated about an axis perpendicular to the plane of the glass.

In such polishing of both surfaces, one of the most important problems is the elimination of ribbon breakage as the ribbon passes through the space between the opposed surfacing tools. It has been found that glass polished according to the method and apparatus disclosed in the above-identified Waldron patent also has a tendency to break along its edges due to uneven pressure from the polishing pads and this is of course highly undesirable.

It has likewise been known, as shown and described in U.S. Patent No. 1,962,766 issued to J. P. Crowley et al. on June 12, 1934, and also as shown and described in US. Patent No. l,l962,767 issued to J. P. Crowley et al. on June 12, 1934, to surface (i.e. grind or polish) the opposed surfaces of a glass ribbon, moving along a definite path, by an oscillating motion of a surfacing unit which includes upper and lower rectangular surfacing runners. This oscillating or orbital motion is applied by rectangular runners whose major dimension is transverse of the path of travel of the glass. The two runners of each unit are further connected so that they will oscillate in unison.

While the apparatus and method shown, described and claimed in the above two Crowley et al. patents is satisfactory for certain purposes, the method and apparatus of the present invention has proven to be of particular utility and has supplied important advantages not available in the structure disclosed in those Crowley et al. patents. It should here be noted that the following description deals largely with the polishing of glass. This is believed to be desirable to facilitate understanding of the invention and is not intended as limiting the invention since it has equal application when simultaneously grinding opposed glass surfaces. The important advantages of the present apparatus, realized by using the method and apparatus of the present invention as compared to the method and apparatus disclosed in these Crowley et al. patents, will be later discussed. However, before proceeding with a detailed description of the method and apparatus of the present invention, it is felt that a preliminary discussion of some of the salient features thereof will facilitate a more complete understanding of these details later appearing.

Broadly stated, the present invention provides a method to simultaneously surface both sides of a glass ribbon moving along a predetermined path by a new and unique control of and application of the surfacing forces.

Generally speaking it could be said that the efficiency of both grinding and polishing action on a glass surface is greater when each point on the glass has been subjected to a great number of surfacing actions exerted from all directions. However, it should be pointed out that this alone will not suflice to provide a mirror finish on the glass since the aforementioned principle is not the eXclusive answer but forms only a part of the complete solution.

For example, it has been found that the lineal speed of the glass ribbon, as the glass is subjected to the working action of a rectangular surfacing tool moving along a path most aptly defined as a curvilinear translation, materially effects the glass finish. In the instant case this curvilinear translation is characterized by the fact that the path of each point on the tool describes a circle. It is contemplated, however, and should be understood that the broad concept of this invention would be applicable to other types of curvilinear translation for example, where the point on the tool followed an elliptical path.

Now, the examination of relative speeds includes a comparison of the speed and magnitude of the curvilinear translation either jointly or singly with this lineal glass path. By the term magnitude it is intended to mean the magnitude of the radius of the path on any point as it follows its certain path. In this regard it is noted that the glass ribbon is moved along a predetermined path under the action of suitable drive means that are themselves capable of delivering variable speeds. Therefore the lineal speed of the glass ribbon moving past a fixed point along the path of the ribbon may be varied between 0 inches per minute and 300 inches per minute. This, in and of itself, might not be considered singularly unique, however, when it is weighed and considered in the light of the further discussion it will become apparent that this variation in linear glass speed supplies an important control over an element or step of the present invention and assists in realizing the resultant superior mirror finish of the glass.

By suitable applicators, a glass surfacing or surface affecting medium is normally applied to both surfaces of the ribbon before or while the ribbon is surfaced. It has been found, however, that this medium should be applied uniformly across the ribbon, as for example, in a curtain. However, no matter what apparatus is used to apply the medium, care must be taken to be sure it is applied in a manner calculated to form a uniform film across all portions of the glass. This has been found to be highly pertinent to insure uniform surfacing of the glass. It is extremely important to insure uniformity of application of the surfacing medium so that when the medium is carried under or between the surfacing tools on the glass, there will not be developed any nonuniform areas of polishing medium to result in uneven glass surfacing.

Broadly expressed, control over the forces developed in the surfacing apparatus has been found to be a major factor establishing the superior mirror finish of glass surfaced according to the present method and apparatus. This is an extremely critical point of distinction, particularly with regard to the prior art typified by the aforementioned Crowley et al. patents, and therefore it is believed it would be desirable to more fully describe this concept of the invention at this point before proceeding with the detailed description.

Now as the glass ribbon passes between the opposed tools it has been found essential to eliminate all vibration transfer between the tools and the glass due to vibration of the tools or flutter of the tools. This is considered very important particularly as regarding breakage of the glass which would result if this vibration transfer became excessive or in fact if it was uncontrolled. This elimination of vibration transfer is also considered important from the standpoint of obtaining the superior mirror finish associated with glass surfaced according to the present invention. To accomplish this the individual surfacing tools of the present invention are balanced with respect to themselves and also with respect to each other so that the resultant forces acting on the glass are controlled and also undesirable forces acting on each surfacing tool or group of surfacing tools are minimized.

Another fact to be taken into consideration is the possible effect on the final glass surface of the wear of the runner surfacing face. In order to adequately control or alleviate this problem of runner wear, the control of the forces developed in the surfacing apparatus must include a fine adjustment or control since, for example, as the tools perform their normal function on the glass the surfacing faces of the tools naturally tend to wear, even if only slightly. However, if this wear were allowed to continue without compensation it could lead to inequalities of surfacing action. Therefore, in order to avoid resultant surface defects attributable to runner wear the surfacing face wear should be overcome. It should be understood that in continued use the surfacing face will have to periodically be replaced, however, in the interim period (i.e. while the runner performs its normal surfacing action) some compensation must be made to overcome the normal wear during use. In this regard it should be noted that normally the runners will wear evenly, however, in order to compensate for possible uneven wear of the runner working face, certain of the hearings in the runner supports have been made self align'ing.

In following further the novel concept of surfacing by the present invention, consider now the forces developed upon, or by, a single grinding runner or platen and its associated supports, there normally being two of the latter for each one of the former regardless of whether or not the runner be in the upper or lower position with respect to the glass being treated.

In the first instance, an examination of a single grinding platen positioned above the glass surface and in a position to surface the upper surface of the continuously moving glass ribbon will reveal the development of certain forces.

As the tool is caused to follow its path, best described as a curvilinear translation by reason of its speed of rotation and magnitude of oscillation, there is developed a force in the plane of the center of gravity of the tool which may be referred to as the centrifugal force of the tool. This force is the radial force of the tool exerted in a-direction outwardly of the circular path of the tool.

Opposing this centrifugal force is a first bearing force developed in the two bearings. This first bearing force is exactly equal to but exerted in the opposite direction to the centrifugal force so that the resultant sum of these two forces is zero. The bearings are located in the plane of the center of gravity of the tool so that this first bearing force is located in the plane of the center of gravity of the tool, i.e. the plane of the centrifugal force.

The next force developed might be referred to as the drag force on the glass, so as to distinguish it from the polishing defect known as drag. This drag force is a tangential force exerted along a line tangent to the circular or orbital path described by the surfacing tool. This drag force is exerted in the plane of the glass surface contacted by the tool and is the force developed by the frictional resistance of the glass to the tool as the tool sweeps thereacross. The drag force, being tangential to the path of the tool is therefore apart from the centrifugal force which as above discussed is a radial force when taken with respect to the path of the tool.

The remaining major force is a second bearing force developed in the same bearings that opposes the centrifugal force. This second bearing force is exactly equal to, but opposite to, the drag force so that the resultant sum of these two forces is actually zero. These bearings as above discussed, are located in the plane of the center of gravity of the tools, so that the first and second bearing forces are exerted in the same plane, i.e. the plane of the centrifugal force.

Now, although the two bearing forces are substantially in the same plane as the centrifugal force (i.e. the plane of the center of gravity of the tool) the drag force is in a different plane (i.e. the plane of the surface of the glass). This could possibly introduce some tendency of the surfacing tool to flutter as it followed its orbital path due to the torque thereby introduced. However, this tendency of the surfacing tool to flutter has been substantially eliminated or at least has been materially reduced by adding counterweights to dampen the effect of the centrifugal force. This dampening of the centrifugal force developed has been found to be extremely effective in overcoming any possible passage of flutter onto the drive mechanism or drive case. In addition, particular attention has been paid to the general machine design with emphasis on its rugged construction so as to further eliminate any possibility or tendency of any flutter developing.

The above features are applicable to both the upper and lower surfacing members and also to a surfacing unit, it being understood that a surfacing unit would be composed of two platens, one above and one below the glass, or four surfacing members, two above and two below the glass. It also should be understood that a plurality of these units, composed of two or four members, could be arranged along the path of the glass and that the above discussion would apply to each member of each unit regardless of the actual number.

In order to compensate for possible misalignment of the tools with respect to the glass because of an uneven or irregular surfacing face on the tools when the tools are arranged on opposite sides of the ribbon, the bearings for the upper tools are self-aligning as aforenoted. In the specific embodiment, to be later described in detail, the plane of action of the bearings is actually only 4 inches above the plane of the glass while the plane of the center of gravity of the tools is about inch above this bearing plane. The bearings for the lower tools are not self-aligning and are fixed. They will of themselves, however, still overcome possible flutter so that the forces induced by the center of gravity and work effort taken with respect to a lower tool can be substantially disregarded, with respect thereto. However, counterweights are also used to dampen any possible forces acting on the driving case of the lower tool.

Now turning to the practical application of the present invention, for each individual member surfacing the upper surface of the ribbon there is a similar Opposed lower member that is arranged to surface the lower surface of the ribbon. As will later be described the upper and lower tools are also positioned so that they move 180 out of phase with respect to each other. This means that the work effort or drag force applied by the upper runner or tool will always be applied in or exerted in a direction opposite to the drag force or work effort of the lower tool. This further establishes the equilibrium of the system and further avoids the possible introduction of any undesirable forces onto the glass.

Positive control over the amount of the work effort or drag force as well as control over the centrifugal force may be secured through the variation of any number of variables but primarily it is gained by altering the speed of spindle rotation or oscillation diameter, for example, it might be desirable, for some reason, to take action effecting the polishing defect known as drag by reducing or increasing the oscillating diameter. It might then, however, become desirable to make a converse alteration of the spindle speed to insure that the total power input to the glass remained the same. These conditions of course, are altered often and the optimum operating conditions will become apparent to the operator as he gains experience under varied conditions.

There has been discussed above the principal manner in which the present method and apparatus has established equilibrium of the apparatus and eliminated the flutter which is associated with conventional surfacing tools. This, of course, will be later explained and discussed in detail. In addition to this, and after establishment of the above described equilibrium, there has been added a system by which it is possible to add, and also to control, the positive working pressure of the surfacing tools, platens or runners on the glass. This gives a positive manner of insuring that only enough working pressure will be applied to the glass to result in the desired finish and that there will be no possibility of developing excessive pressures which might cause the ribbon to break.

There has, therefore, been provided a novel method of and apparatus for surfacing glass which has overcome the deficiencies of the prior art and resulted in an exacting quality finish upon both surfaces of the glass which surfaces are acted upon at the same time. Having broadly discussed the basic features of the applicants polishing device it should be remembered that other salient and novel features will be hereinafter discussed which features individually effect one or more of the above principles.

As the specification proceeds it will be appa-rent that individual surfacing units of the present invention include two surfacing tools above the ribbon and two surfacing tools below the ribbon and that a plurality of these units are arranged in succession to provide continuous surfacing of a continuous ribbon. More particularly every individual surfacing tool will have its movement synchronized to either an adjacent or an alternate tool and likewise alternate or adjacent successive units are synchronized so as to establish an equilibrium condition among all the units and members of each unit. This concept of proper control over the forces acting on the glass and those developed within the units themselves lie at the very heart of this novel method and apparatus for surfacing glass and should be interpreted in the light of the description that follows.

Therefore, according to the present invention, there has been provided a method and apparatus for surfacing glass wherein the various contributing factors that influence the final finished surface on the glass have, to a great extent, all been considered and thereby a novel method and apparatus developed, to ove-rcome the deficiencies, above discussed, of the prior art. The result is, therefore, a method and apparatus that will produce a mirror finish on both surfaces of the glass which is a finish of the highest quality.

It is therefore a primary object of the present invention to provide an improved method for surfacing both sides of a continuous glass ribbon which will achieve an improved surface finish on the glass ribbon.

It is another object of the present invention to provide for control over all the forces applied to the glass surfaces in order to maintain these forces above and below the ribbon in a balanced condition.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIG. 1 is a schematic drawing of twin station apparatus for simultaneously polishing both surfaces of an advancing ribbon of glass;

FIGS. 2, 3, 4 and 5 are schematic side elevations progressively illustrating lowering of the upper polishing platen from its maximum raised position to its polishing position;

FIG. 6 is a plan view of the apparatus;

FIG. 7 is a side elevation of the apparatus as viewed from the right of FIG. 6;

FIG. 8 is a cr-oss-section taken on the line 8-8 of FIG. 6;

FIG. 9 is a vertical cross-section of an upper platen support head taken on the line 99 of FIG. 6 showing the telescoping cylinder and the platen drive mechanism;

FIG. 10 is a vertical cross-section of an upper platen support head taken on the line 10-10 of FIG. 6 showing the head elevating mechanism, the glass breakage safety stop and a portion of the safety stop clearance indicator mechanism;

FIG. 11 is a section taken on the line 11-11 of FIG. 10 showing the telescopic shaft arrangement for the safety stop clearance indicator;

FIG. 12 is a section taken on the line 12-12 of FIG. 10 showing the relation of the glass breakage safety stop and the clearance indicator take-off;

FIG. 13 is a cross-section of a portion of the safety stop taken on the line 13-13 of FIG. 12;

FIG. 14 is a section of a portion of the safety stop and clearance indicating mechanisms taken on the line 14-14 of FIG. 12;

FIG. 15 is a fragmentary section of the clearance indicating mechanism taken on the line 15-15 of FIG. 14;

FIG. 16 is an elevation with parts in section taken substantially on the line 16-16 of FIG. 6 showing the pneumatic apparatus for supporting the weight of the upper platen and applying a metered pressure to the upper surface of the glass;

FIG. 17 is a vertical section of a lower head showing the platen drive and elevator mechanisms;

FIG. 18 is a cross-section taken on the line 18-18 of FIG. 17;

FIG. 19 is a cross-section taken on the line 19-19 of FIG. 17;

FIG. 20 is a cross-section taken on the line 20-20 of FIG. 17 showing the detailed construction of an eccentric;

FIG. 21 is a section of an eccentric taken on the line 21-21 of FIG. 20;

FIG. 22 is a section of an eccentric taken on the line 22-22 of FIG. 20;

FIG. 23 is a section of an eccentric taken on the line 23-23 of FIG. 20;

FIG. 24 is a section of an eccentric taken on the line 24-24 of FIG. 21;

FIG. 25 is an enlarged detail of the switch apparatus for limiting the raising and lowering of a lower platen head;

FIG. 26 is a section taken on the line 26-26 of FIG. 8 showing a plan view of the divided platen;

FIG. 27 is a vertical section taken on the line 27-27 of FIG. 26 showing an upper and a lower polishing platen contacting opposite surfaces of the glass and respectively joined to an eccentric drive member; and

FIG. 28 is a section of a portion of the platen taken on the line 2828 of FIG. 26.

General description Preliminary to a complete description of the apparatus, reference is made to the schematic diagrams, FIGS. 1 through 5.

A ribbon of glass 40 is continuously advanced at one of a comparatively wide range of speeds in the direction of the arrow 41 through a plurality of polishing stations, two of which are indicated by the letters A and B. Each station is comprised of apparatus 42 for polishing the upper surface of the glass and apparatus 43 for polishing th lower surface of the glass.

The upper surface polishing apparatus 42 includes a rectangular polishing platen 44, including a felt working face, secured adjacent each end to an eccentric drive mechanism 45 driven by a variable speed motor 46 which imparts to the platen a curvilinear translation, or a circular orbital motion along a closed path, preferably in a clockwise direction as indicated by the arrow 47 in FIG. 1. Also, as shown in FIG. 1, the two eccentric drive mechanisms 45 for each platen 44 are in angular alignment so that the ends of the platens 44 remain parallel to the edges of the glass ribbon 40 at all times.

In FIGS. 2 through 5, the upper platen 44 is raised or lowered with respect to the ribbon of glass by telescoping a part of the eccentric drive mechanism 45, as generally indicated by the numeral 48. Lowering of the upper platen from the FIG. 2 to the FIG. 3 position is accomplished by motor 49 while further lowering from the FIG. 3 position to the glass contacting position of FIG. 4 is done manually by rotating a crank 51. Raising of the upper platen 44 is in response to a glass ribbon breakage detection device such as a switch 52 or to a manually operated switch (not shown) wired in parallel to the switch 52. The motor 49 is reversibl and designed to lower the platen 44 at a low rate and to raise the platen at a fast rate.

Pneumatic operated apparatus 53 is mechanically connected to balance the weight of the upper platen 44 and those portions of the eccentric drive mechanisms 45 which are not supported by the framework and to apply a metered polishing pressure within a range of to 4 psi. upon the top surface of the glass. The value represents the contact pressure developed between the surfacing tools and the ribbon surfaces opposite thereto. The pneumatic control apparatus for balancing the weight of the upper platen and drive mechanism and applying pressure to the top surface of the glass ribbon 40, are respectively indicated by the numerals 54 and 55 and respectively are in communication with the top and the bottom of a cylinder 56. Upon breakage of the ribbon of glass 40, the switch 52 acts to relieve the pressure within the cylinder 56 simultaneously with the previously mentioned energization of the motor 49 for rapidly elevating the platen.

Realizing that a slight time lag will occur between the breaking of the ribbon of glass 40 and the raising of the upper platen 44, during which time the platen will drop, a mechanical safety stop 57 is incorporated into the upper platen elevating mechanism 50. The safety stop 57 will arrest the descent of the upper platen 44 upon breakage of the ribbon 40 before contact is made with the lower platen 58. An indicator 59 is calibrated in thousandths of an inch to permit the operator to adjust the safety stop apparatus 57 so that it will halt the descent of the upper platen 44 before it contacts the lower platen 58.

The lower glass surface polishing apparatus 43 is simpler than the upper glass surface polishing apparatus 42. The lower platen 58 is substantially identical with the upper platen 44, the only changes being those normally employed to compensate for the respective forces applied thereto. An eccentric drive mechanism 60 is connected to each end of the lower platen 58 to cause the lower platen to move according to a curvilinear translation equal 8 in magnitude to the motion of the opposed upper platen 44, but out of phase with the orbit of the upper platen. A selsyn system, generally indicated by the numeral 61, is provided to synchronize the orbital motions of the upper and lower platens, comprising each station, 180 out of phase relation.

The eccentric drive apparatus 60 for the lower surface polishing apparatus 43 is connected to a variable speed drive motor 62 and also to a reversible motor 63 for raising and lowering the lower platen 58. A bench mark is provided at each station to assist the operator in determining the initial level for each lower platen 58 and also serves as an indicator for determining when correction of the elevation of the platen 58 is required to compensate for wear of the platen polishing pad.

As is indicated in FIG. 6, a second selsyn system 64 is provided to synchronize the rate of the polishing platen at adjacent stations. As previously disclosed, the upper and lower platens 44 and 58 at any one station are each caused to move in a clockwise circular orbitof equal magnitude and at a synchronized speed, 180 out of phase. When the eccentric drives of adjacent stations, as A and B, are synchronized by the second selsyn system 64, the motion of the upper platens 44 at adjacent stations and the lower platens 58 at adjacent stations (i.e. each unit composed of two upper and lower platens) are also operating 180 out of phase, as is shown in FIG. 1, and this relationship will remain as long as the platen speeds at adjacent stations are synchronized.

In other words, the upper platen 44 of any station A is moving in phased relation to the lower platen 58 of an adjacent station B, when those two stations A and B are synchronized by the selsyn system 64. However, it is also noted that the upper platens 44 of adjacent stations A and B are out of phased relation 180 with respect to each other.

Now due to the varying characteristics of the surfacing medium feeding of these upper platens (i.e., those factors which would include quantity, density or composition) the feed has been found to be somewhat less than continuously uniform over an extended period of time. In order to overcome the undesirable effects of these variables upon the glass finish, it has been found that the offset of the upper platens and also the offset of the lower platens (i.e., their different phased relation) is an important element achieving uniform glass finish. This is true since it has been found that by offsetting the upper platens (and also incidentally the offsetting of the lower platens) that this offset will balance or overcome the undesirable forces acting to the ribbon attributable to incidental feed variations. Thus the platen offset will keep any extraneous motion of the ribbon within operational requirements.

An initial examination of the polishing system. shows that there are four variables present effecting the efificiency of the polishing operation. These variables are broadly expressed as follows:

(1) The frequency of the orbital motion or curvilinear translation of the platens at each station. This frequency may be varied between substantially 75 and 600 r.p:m.s.

(2) The lineal advance of the glass ribbon. This may be varied from between 0 and 300 inches per minute.

(3) The magnitude of the orbital motion or curvilinear translation of the platens at each station. This may be varied from substantially between 0 to 4 inches (diameter) for each individual platen independent of any other platen. Normally opposed platens at one station A or B will have the same magnitude of orbit but if desired they may have different orbital magnitudes. Likewise, the platens at adjacent stations A and B normally have the same magnitude of orbit, however, they may have different orbital magnitudes, the variation being determined, for example, according to the grade of glass finish desired.

(4) The load pressure of each platen on the glass ribbon, i.e. the contact or load pressure developed between the felt and the glass. This may be varied between substantially and 4 psi.

Four variables are thus present; namely (1) the fre quency of the orbital motion of platens at each station may be varied between 75 and 600 rpm, (2) the lineal advance of the glass may be varied from 0 to 300 inches per minute, (3) the magnitude of the orbit may be varied from O to 4 inches, and (4) a variable load pressure selectable between 0 to 4 p.s.i. The combination of the lineal advance of the ribbon of glass and the orbital motion of each platen will generate a polishing curve upon the surface of the glass which is cycloidal. It is evident therefore that the first three variables will each directly modify the polishing curve in a particular manner and that in combination these variables permit many minute variations in the character of the final polishing curve within a wide range. It is believed that the range specified above for each variable is suificiently comprehensive for all foreseeable glass polishing requirements and each is primarily cited as an example, which is not to be construed as limiting the scope of the invention.

Generally speaking, the magnitude of the orbital motion and the load pressure determine the maximum work done by the polishing platen and are basically con sidered to be a. function of the power of the machine. Thus, it might be said that if the first three variables above listed were established and remained constant, the maximum work of the platen could be varied, due to specific conditions and desirable polishing finish characteristics required, by control over the load pressure. One example of this would be varying the load pressure according to the different polishing mediums used with the platens. This would follow because different polishing mediums would develop different coefficients of friction between the glass and felt thereby effecting the drag of the platen across the glass and also the glass finish. The greater the coefficient of friction, the less power needed and hence a reduction in the load pressure would be needed. Should the coefiicient of friction be reduced, it would be possible to increase the power by increasing the load pressure. Thus it could be said that variations of the load pressure would be the best way of varying the power put into the machine.

In general summary as shown in FIGS. 7 and 8, the stations A and B are supported in pairs with the upper surface polishing apparatus 42 supported on a framework 65 and the lower surface polishing apparatus 43 supported on a framework 66. The framework 65 is provided with a plurality of motor driven pinch rolls 67 transversely contacting the upper and lower surfaces of the ribbon of glass between each pair of stations A and B to advance the ribbon in the direction of the arrow 41,

Drive for upper polishing heads The upper surface polishing apparatus 42 is supported on the framework 65 and includes a pair of polishing heads 68 suspended in spaced relation inside the opposed edges of the ribbon of glass 40.

The construction of the telescopic drive mechanism of each upper head is shown in detail in FIG. 9. A cylinder 69, having bore 70 open at the bottom end 71 and closed at the top end by a gear case 72, is supported by the framework 65. A worm gear 73 is mounted on a hollow spindle 74 which in turn is supported within the gear case 72 by bearings 75 and 76 for rotation on the extended centerline of the bore 70. A worm 77 is in engagement with the worm gear 73 and is fastened to a shaft 78 (FIG. 8) which projects inwardly through the gear case 72 to connect with the shaft 79 of the double-ended drive motor 46 through a flexible coupling 80. As is clearly shown in FIGS. 1, 6 and 8, the motor 46 is double-ended and is connected as described above to drive two upper polishing heads 68 which are connected to a single polishing platen 44 in a manner to be disclosed hereinafter. The worm gear spindle 74 is provided with a circular opening 81 in its base and a vertically extending groove 82 cut into the inner surface of the wall 83 of the spindle 74. A coupling 84 is keyed to a shaft 85 and the coupling is provided with a projection 86 for vertical movement in the groove 82. A sleeve 87 is supported on the shaft 85 for vertical movement in the bore 79 and is provided with bearings 88, 89 and 90 to support the shaft 85 for rotation within the sleeve and to absorb the thrust. An eccentric, generally indicated by the numeral 91, depends from the lower end of the shaft 65 and will be described in detail hereinafter.

Thus, regardless of the elevation of the eccentric drive mechanism 45, each of the shafts 85 of the two upper surface polishing apparatus 42 is engaged for rotation at identical speeds and direction by the drive motor 46 within the range of 75 to 600 rpm.

Elevating mechanism for upper head The uper head elevating mechanism is generally indicated by the numeral 50 and although it is closely related to the safety stop mechanism 57 (i.e. some of the parts of each, are common to both) the following description is substantially restricted to the elevating mechanism 50.

As described in conjunction with the drive mechanism for the upper heads, the sleeve 37 is mounted for vertical movement within the cylinder 69 and the shaft 85 carrying the eccentric 91 is rotatably mounted within the sleeve for vertical movement but with the groove 82 and the projection 86 in driving engagement.

Referring particularly to FIGS. 10 and 12, a circular opening 92 penetrates the side wall of the sleeve 87 and an open ended hollow cylinder 93 is piloted or slipped into the opening flush with the outer wall of the sleeve 87 and projecting into the sleeve in a direction normal to the axis of the sleeve for a distance approximating one-half the radius of the sleeve. The bore 94 of the hollow cylinder 93 provides a snug bearing for the cylindrical end 95 of a lift block 96. At the opposite end of the lift block 96 is an enlarged rectangular section 97 terminating in a pair of vertically extending ears 98 (FIG. 12). The enlarged rectangular section 97 of the lift block 96 extends through a vertically extending opening 99 in the side wall of the cylinder 69 thereby providing for vertical movement of the lift block 96 with the sleeve 87. The lift block 96 is also provided with a screw slot 100 (FIG. 13) and a counterbore 101, both elongated in a vertical direction as shown in FIG. 13, for a purpose which will become apparent hereinafter.

A housing 102 is attached by screws to the outer surface of the cylinder 69 in alignment with the lift block 96 and is provided with a pair of ways or guides 103 ex tending vertically in spaced relation, as illustrated in FIG. 12.

A second lift block 104 is in engagement with a helically threaded shaft 165 and is held against rotation by the ways 103. One end of the second lift block is nested within the ears 98 of the first lift block 96 and is provided with a pair of horizontally extending ears 106 in overlapping relation to the rectangular end section 97 of the first lift block 96. The span between the ears 106 is sufficient to provide a clearance 107, which is best shown in FIG. 14. The reason for providing. this clearance will be disclosed in conjunction with the safety stop mechanism 57. A shoulder screw 108 joins the lift blocks 96 and 104 passing through the slot 100 and counterbore 101 to engage a threaded opening in the lift block 104.

The threaded shaft is mounted for rotation in bearings 109 provided in the top and bottom of the housing 102 and the lower end of the shaft is extended at a reduced diameter to carry a miter gear 110 which is in engagement with another miter gear 111. The miter gear 111 is in turn fastened to a shaft 112 which is joined to one of the output shafts 113 of the double-ended motor 49 by suitable couplings 114, as shown in FIGS. 1 and 8. FIGS. 1 and 8 also show an extension of the shaft 112 at one end for engagement by a crank 51 to raise and lower the pair of eccentric drive mechanisms 45 comprising a polishing station.

Attention is again directed to the characteristics of the motor 49, namely, it is a two-speed reversible motor adapted to lower the platen 44 at the slower speed and to raise the platen 44 at a higher speed.

Rotation of the motor 49 in either direction imparts a rotary motion to the shaft N (FIGS. 1 through 5 and 10) which moves the lift block 104'; in a vertical direction carrying the shaft 85 with it. Rotation of the motor 49 in one direction, lowers the shaft at a slow rate within the limits defined by FIGS. 2 and 3. Further descent is accomplished by rotating the crank 51. R0- tation of the motor 49 in the opposite direction, raises the shaft 85 at a faster rate from the FIG. 4 position to the FIG. 2 position.

Apparatus for regulating polishing pressure The apparatus for regulating polishing pressure, generally indicated by the numeral 53 in FIGS. 1 through 7 and 16, is pneumatic and is designed to independently support the weight of the upper surface polishing apparatus 42 and to provide a polishing pressure upon the top surface of the glass ribbon 40.

Referring to FIG. 16 in particular, a vertically extending slot 115 penetrates the side wall of the sleeve 87 and receives an insert 116 which is provided with a seat 117 for a gear rack 118. The teeth of the gear rack extend horizontally, flush with or slightly inside the outside diameter of the sleeve 37. Screws 111 retain the gear rack 118 in the seat 117. Another recess 12% is provided in the outer face of the insert 116 and extends downwardly from the bottom of the gear rack 118 for a distance slightly greater than the vertical travel of the sleeve 87. A rectangular opening 121 extends through the wall of the cylinder 69 at a point in alignment with the gear rack 118 when the sleeve 87 is at and near its lowermost position. A pair of brackets 122 are attached with screws to the outer surface of the cylinder 6%, one on either side of the opening 121, to support a gear segment 123 on a pivot 124 with the teeth of the segment pivotable into and out of engagement with the teeth of. the gear rack 118. The end of the gear segment 123 opposite the teeth is pivotably fastened by a pin 125 to the piston rod 126 of the double-acting pneumatic cylinder 56. The cylinder 56 is in turn pivoted on trunnions 127 projecting from the pneumatic cylinder 56 adjacent the top thereof and fastened to the outer surface of the cylinder 69 by means of a bifurcated bracket 128 positioned vertically above the gear segment 123. A flexible hose 129 admits air from a manually controlled source 54 to the top of the cylinder 56 and a second flexible hose 130 from a second manually controlled source admits air to the bottom of the cylinder.

Referring, in addition to FIG. 16, to FIGS. 2 through 6, each pair of hoses 129 at a polishing station are attached to a header 131 (FIG. 6) to which pressure is applied from the manually activated pneumatic balancing apparatus 54. As is shown in FIG. 16, the gear segment 123 provides a 2 to 1 mechanical advantage which reduces the pressure requirements in the cylinder 56 for balancing the weight of the upper platen 44 and the unsupported portion of the eccentric drive mechanisms 45. When the platen 44 is in the raised position of FIG. 2, a relatively small pressure is exerted on the top of the piston in the cylinder 56 to maintain the piston rod 126 in the extended dashed line position shown in FIG. 16 so that the gear segment 123 will be in position to engage the rack 118 upon lowering of the platen 44.

In the same figures, each pair of hoses at a polishing station are attached to a header 132 (FIG. 6) to which pressure is applied from the manually activated pneumatic apparatus 55'.

Thus, in the positions shown in FIGS. 2, 3 and 4 the weight of the platen and the eccentric drive mechanisms are supported by the lift mechanism 59. However, as pressure (approximately 56 p.s.i.g.) is applied to the cylinder 5s above the piston, the weight is supported by the pneumatic apparatus 53, and, as illustrated in FIG. 5 and at an enlarged scale in FIG. 14, the relative position of the lift blocks and 1% has shifted so that the clearance 167 which had previously been at the top is now at the bottom, as is shown in dashed lines. This pressure is referred to as weigh pressure.

Thereafter air is admittted to the lower portion of the cylinder 56 below the piston to direct a downward force on the shaft applying a polishing pressure to the glass This pressure is referred to as load pressure, and when referenced to the area of felt on the platens will be in the range of (l to 4 psi. In other words load pressure is the amount of air pressure required to subject each square inch of felt, in contact with ribbon, to a pressure within the range of 0 to 4 pounds. This figure designates the contact or load pressure between the felt and the glass so that by analogy it could be said that the ribbon would be pinched between the upper and lower platens. The application of this load pressure will tend to return lift block 96 to its original position with respect to lift block 1% (FIG. 14) before application of the weighing pressure. With proper location of the safety stop apparatus, to be explained in detail later, a controlled amount of clearance will be indicated on clearance dial 5) and thus dial 5S will show the distance a platen 24 would drop in case glass ribbon 4A1 breaks.

Safety stop apparatus and clearance indicator The elements of the safety stop apparatus 57 also are a part of the lift mechanism 51 In operation as the upper platen E4 is lowered by motor 4% from a position shown in FIG. 2 and FIG. 3 (re-engagement of the pneumatic system 53) and to a position approximately 1 inch above the top surface of the glass ribbon 41). At this point limit switch opens the motor lowering circuit by contact with lift block 164, and the foregoing weigh pressure is applied to cylinder 56. To lower upper platen 44 the remaining 1 inch to contact glass ribbon 41 hand crank 5'1 (FIG. 1) must be used. Rotation of this hand crank in proper direction will lower lift block 104 on which lift block 96 is bearing. As the felt attached to the ribbon platen contacts the glass ribbon, the platen 44- comes into physical rest upon the ribbon 40, the ribbon 41) itself being supported by the lower platens. Therefore, further downward travel of spindle 85 and lift block 96 is prevented. At this point additional rotation of hand crank 51 will lower the lift block 104 with respect to lift block 96. Once the lift block 104 is properly positioned with respect to lift block 96 to gain the proper clearance then the proper load pressure, as aforedefined may be applied.

It is obvious that breakage of the ribbon of glass 40 poses a serious problem in that the upper platen must be stopped short of contact with the lower platen 58 to prevent damage to the platens. Therefore, the clearance 19-7 is initially set, by proper regulation of lift :block 104, with respect to lift block 96 so that the dashed line clearance 1117 is appreciably less than the thickness of the ribbon of glass 40. Periodic adjustments of this clearance relationship must be made to compensate for reduced thickness of the platen 4 1- due to wear.

Since it is not feasible to measure the clearance 107 at a plurality of stations and at points positioned on both sides of a rather long machine, a clearance indicator 59 with two pointers has been provided on one side of the 

1. IN A METHOD OF SIMULTANEOUSLY SURFACING BOTH SIDES OF A GLASS SHEET MOVING ALONG A PREDETERMINED PATH, WHEREIN SAID SHEET IS PASSED INTO AND THROUGH THE SPACE DEFINED BY A PLURALITY OF PAIRS OF OPPOSED, GENERALLY RECTANGULAR SURFACING MEMBERS, WITH EACH MEMBER BEING IN SURFACING ENGAGEMENT WITH A SIDE OF THE GLASS SHEET ADJACENT THERETO AND DRIVEN THROUGH MEANS EFFECTIVE TO IMPART A CURVILINEAR TRANSLATION TO EACH MEMBER SUCH THAT THE LONGITUDINAL EDGES THEREOF REMAIN SUBSTANTIALLY NORMAL TO THE PATH OF MOVEMENT OF THE GLASS SHEET DURING THE SURFACING OPERATION, THE IMPROVEMENT COMPRISING DRIVING ALL OF THE SURFACING MEMBERS IN THE SAME DIRECTION AND SYNCHRONIZING THE MOTION OF OPPOSED SURFACING MEMBERS OF EACH PAIR SUCH THAT THEY ARE 180* OUT OF PHASE WITH RESPECT TO ONE ANOTHER AND ALSO SUCH THAT THE UPPER SURFACING MEMBER OF ONE PAIR IS IN PHASE WITH THE LOWER SURFACING MEMBER OF THE PAIR OF PAIRS IMMEDIATELY ADJACENT THERETO. 